We have a 12 x 22 x 24" deep pond. It has had 9 koi and a variety of
goldfish, now over 10 years old. The koi have thrived and grown
huge. Thay cruise around happily, breed like mad and eat like pigs.
If your pond does not freeze solid and you keep some air in the
winter, they should do well with your depth and size. Have a good
filter setup. They will stir a smooth bottom and sweep the muck to
the low points. Have a blast!

Jim